A system for protecting the battery of a vehicle includes a device (1) for electrically disconnecting of connecting the battery (BA) with respect to an electric load (CS). The device (1) includes a switch (20, 21) and a microprocessor control circuit (15). The control circuit (15) includes a unit for calculating a mean value of the voltage of the battery (BA) and comparing it with a threshold value, in order to control the switch (20, 21). The threshold value is variable as a function of the ambient temperature and the time of inactivity of the motor. The switch includes a bistable electromagnetic arrangement, capable of passing from a first to a second stable condition following a pulse generated by the control circuit (15).